Will Labour commit to referendum on any Brexit proposed by this government?

Sources close to the Labour leader believe the emergency NEC meeting on Tuesday, which determines the Labour manifesto for the EU elections, will agree a formula that is "a restatement" of the party's equivocal and prolix party conference resolution of last September.

But a senior trade union source tells me that if Unison, GMB and Usdaw are bulldozed on Tuesday, if their demand for Labour to commit to a "confirmatory" referendum on any Brexit deal is simply ignored, Corbyn and his colleagues are "being delusional about the likely consequences".

The well-placed trade unionist added: "They have no idea what's going to hit them and the scale of the backlash they will face" - which captures for you how emotions are running very high.

And given that Unison, the GMB and Usdaw are respectively the first, third and fourth biggest trade unions in the UK, they can certainly cause trouble for Corbyn, if so minded.

So is there a compromise that would allow honour to be satisfied on both sides?

Keir Starmer and Tom Watson want Labour's manifesto to call for a public vote. Credit: PA

Well one idea being touted is that Labour could put in its manifesto that there should be a referendum on any Brexit deal proposed by the government this side of a general election, or a confirmatory public vote on what would be characterised as a "Tory" Brexit deal.

As the founder of Momentum Jon Lansman implied on Sunday, that would be consistent with part of the epic conference resolution, since it included the phrase that "if the government is confident in negotiating a deal that working people, our economy and communities will benefit from they should not be afraid to put that deal to the public".

It also said: "When trade unions have a mandate to negotiate a deal for their members, the final deal is accepted or rejected by the membership" - which again implies that Labour's preference is for a confirmatory ballot.

The looming European elections are casting a shadow over cross-party efforts to find a Brexit compromise. Credit: PA

The big point is that a Labour pledge to campaign for a confirmatory referendum on any Brexit shaped by Theresa May or her successor, this side of the next general election, would be consistent with existing Labour policy, even if it would be considerably clearer and less ambiguous than the current position.

It would allow Labour candidates for the EU parliament to say, without keeping their fingers crossed behind their back, that they and their party are in favour of a referendum, which most of them say is precisely what they need and want.